The present invention relates to an image forming apparatus for forming an image on a specific recording medium according to input data.
In a conventional image forming apparatus, before an image forming process is conducted, a thickness of a recording medium to be printed is measured, and a process value suitable for the thickness is determined. More specifically, in a conventional image forming apparatus, a table containing an optimized transfer voltage, an optimized developing voltage, an optimized fixing temperature, and the likes is created in advance. According to a thickness of a recording medium, a process value such as a transfer voltage, a developing voltage, a fixing temperature, and the likes is determined with reference to the table (refer to Patent Reference).
In the conventional image forming apparatus, every time when a recording medium is supplied, a thickness thereof is measured. Alternatively, only the first one of recording media stored in a sheet supply tray is measured. In the conventional image forming apparatus, it is necessary to stop a recording medium for measuring a thickness thereof. Accordingly, every time when a thickness of a medium is measured, a process time is delayed by about 0.5 second. For this reason, in most cases, unless a sheet supply tray is exchanged, only a first one of recording media stored in a sheet supply tray is measured under an assumption that a same type of recording media are stored in the sheet supply tray.
Patent Reference; Japanese Patent Publication No. 10-171192
In the conventional image forming apparatus, it is difficult to determine whether a sheet supply tray is exchanged when the image forming apparatus is turned on. Accordingly, it is necessary to always measure a thickness of the first one of recording media, thereby taking a long period of time to form an image on the first one of the recording media.
Further, in the conventional image forming apparatus, a fixing device is heated up to a temperature suitable for a thickness of a recommended sheet upon turning on the power, so that it is possible to start an image forming operation immediately after the power is turned on. Accordingly, it takes a long period of time to heat up the fixing device. Further, in the conventional image forming apparatus, when the temperature of the fixing device exceeds a target temperature, it is necessary to take 30 seconds to one minute for decreasing the temperature (cooling down the fixing device).
Further, depending on an area, a location, or a country, a recording medium having a thickness smaller than that of the recommended sheet may be commonly used. In this case, when the image forming apparatus forms an image on the first sheet after the power is turned on, it is necessary to cool the fixing device, thereby causing at least 30 seconds time loss.
Recently, in order to reduce power consumption, many users tend to turn off the image forming apparatus more frequently, and the image forming apparatus may be provided with a sleep mode. In this case, after the power is turned on, or the image forming apparatus returns from the sleep mode, it takes a long period of time to form an image on the first recording medium.
In view of the problems described above, an object of the invention is to provide an image forming apparatus capable of forming an image on a first recording medium in a short period of time after the power is turned on, or the image forming apparatus returns from the sleep mode.
Further objects and advantages of the invention will be apparent from the following description of the invention.